The design of effective country-wide Chagas disease control programs depend on the understanding of the different factors that play a role in the maintenance and transmission of Trypanosoma cruzi. A clear comprehension of the transmission dynamics of this parasite and its relationship to its vector and reservoir species is crucial for the design of control measures aimed at stopping transmission to humans. The predominant T. cruzi vector species in Northern South America occupy both sylvatic and domestic habitats. As sylvatic vectors become domiciliated, blood sources in the peridomestic environment serve as a bridge between the sylvatic and domestic cycles of transmission. Interaction between sylvatic and synanthropic vectors and mammalian reservoirs favors the constant exchange of parasite strains and their transmission to humans. We hypothesize that the T. cruzi II (TCII) lineage will predominate in domestic habitats, and the TCI lineage will become more prevalent as habitats move from domestic to peridomestic to sylvatic habitats. In addition, we also hypothesize that there is high genetic similarity among parasites isolated from different hosts collected in the domestic, peridomestic and sylvatic habitats in Southern Ecuador, indicating frequent parasite exchange. We will test these hypotheses by: (1) molecularly characterizing T. cruzi isolates from different hosts at domestic, peridomestic and sylvatic environments in Southern Ecuador and (2) determining their genetic similarity; (3) Finally, in order to understand the biotic and abiotic factors that influence gene flow between parasite populations, we propose to examine the relationship between genetic distance and geographical distance. To accomplish these aims we will collect triatomines, mammalian reservoirs and human blood in a set of rural communities located in different ecological zones within Loja Province, in Southern Ecuador. We will isolate and molecularly characterize T. cruzi from these sources using PCR amplification of the non-transcribed spacer regions of the mini-exon gene, 24Sa rRNA and 18Sa rRNA. In addition we will determine the genetic flow among parasite populations infecting the different hosts by analyzing up to 11 polymorphic microsatellites loci in conjunction with the construction of phylogenetic trees. Finally, we will use geostatistical techniques to examine the relationship between the genetic and spatial distances of the various T. cruzi isolates. In addition to helping understand the transmission cycles of T. cruzi, this project will provide excellent training opportunities for undergraduate, graduate and medical students while fortifying the PI's research program and strengthening the institutional research environment, thereby fulfilling the goals of Academic Research Enhancement Award (AREA). The results of this project will add to the existing basic biological knowledge base and contribute towards the National Institute of Allergy and Infectious Diseases' (NIAID) mission of understanding and preventing infectious diseases and thus, improving the health of millions of people in the United States and around the world. PUBLIC HEALTH RELEVANCE: Infection with the parasite Trypanosoma cruzi threatens 100 million people in Latin America, and constitutes a major cause of heart disease in this region. The proposed project will examine the transmission cycles of this parasite Southern Ecuador, which is representative of a vast region of South America where the biological factors affecting T. cruzi transmission have been scarcely studied in the past. The proposed research will expand the knowledge regarding the biology of T. cruzi transmission in the Andean region, which is paramount for the establishment of control programs aimed at stopping transmission of the parasite to human populations. [unreadable] [unreadable] [unreadable]